The skeletal system includes many long bones that extend from the human torso. These long bones include the femur, fibula, tibia, humerus, radius and ulna. These long bones are particularly exposed to trauma from accidents, and, as such, may be fractured during a trauma.
Often the distal end or proximal portions of the long bone, for example the femur and the tibia, are fractured into several components and must be realigned. Mechanical devices, commonly in the forms of pins, plates, screws, nails, wires and external devices are commonly used to attach fractured long bones. The pins, plates, wires, nails and screws are typically made of a durable material compatible to the human body, for example titanium, stainless steel or cobalt chromium.
Subtrochanteric and femoral shaft fractures have been treated with the help of intramedullary rods or nails, which are inserted into the marrow canal of the femur to immobilize the femur parts involved in fractures. Subtrochanteric and femoral shaft fractures of femurs are often accompanied by fractures of the femoral neck and head. Areas around the greater trochanter and lesser trochanter may also fracture. Intramedullary rods or nails are often provided with openings for receiving transverse screws which are used to secure the femoral bone fragments, for example the greater trochanter, the lesser trochanter, the neck, and the head.
When securing bone fragments of the neck and head of the femur, a transverse screw, for example in the form of a lag screw, is fitted through an opening in the intramedullary nail and is screwed into the neck and head of the fractured femur. A solitary screw may permit the bone fragments of the neck and head of the femur to rotate about the screw and, thus, not be properly secured. Maintaining the position of the fragments of the fractures of proximal femoral fractures and trochanteric fractures is important for obtaining good reduction to promote healing. It is important that the bone fragments stay in close proximity to each other or to be in reduction to promote the healing. To assist in proper reduction of the neck and head of a femur, a second screw in the form of, for example, an anti-rotation peg or screw is positioned in a second opening in the intramedullary nail to provide a more rigid construction for securing the fractured bone fragments of the femoral neck and head.
To promote the healing of bone fractures and according to Wolfe's Law the healing of bone fragments is promoted by providing some load or force upon the reduction or fracture site. Such loading of the fracture site promotes healing. Therefore intramedullary nails have been designed to provide for sliding compression or movement of the screws in the openings of the intramedullary nail. Such threading movement of the screw in bone is undesirable. Further, when utilizing a lag screw and an anti-rotation screw in an intramedullary nail, a phenomenon known as the “z effect” may occur. The z-effect occurs when the lag screw or the anti-rotation screw moves in a first direction and the other of the lag screw and the other rotation screw moves in the opposing direction. With the z-effect one screw moves toward the lateral femoral shaft wall while the other screw moves toward the femoral head. Further, while it may be desirable to provide for sliding compression in an intramedullary nail to promote healing, desires to avoid the z-effect and other patient indications may make the use of a locked nail assembly preferred. In a locked nail assembly the transverse screws are rigidly secured to the nail. Therefore, it would be advantageous to provide an improved intramedullary nail assembly.